Synchronize threads using event flags. More...

Data Structures
struct	osEventFlagsAttr_t
	Attributes structure for event flags. More...

Typedefs
typedef void *	osEventFlagsId_t

Functions
osEventFlagsId_t	osEventFlagsNew (const osEventFlagsAttr_t *attr)
	Create and Initialize an Event Flags object. More...

uint32_t	osEventFlagsSet (osEventFlagsId_t ef_id, uint32_t flags)
	Set the specified Event Flags. More...

uint32_t	osEventFlagsClear (osEventFlagsId_t ef_id, uint32_t flags)
	Clear the specified Event Flags. More...

uint32_t	osEventFlagsGet (osEventFlagsId_t ef_id)
	Get the current Event Flags. More...

uint32_t	osEventFlagsWait (osEventFlagsId_t ef_id, uint32_t flags, uint32_t options, uint32_t timeout)
	Wait for one or more Event Flags to become signaled. More...

osStatus_t	osEventFlagsDelete (osEventFlagsId_t ef_id)
	Delete an Event Flags object. More...

const char *	osEventFlagsGetName (osEventFlagsId_t ef_id)
	Get name of an Event Flags object. More...

Description

The event flags management functions in CMSIS-RTOS allow you to control or wait for event flags. Each signal has up to 31 event flags.

A thread

can wait for event flags to be set (using osEventFlagsWait). Using this function, it enters the BLOCKED state.
may set one or more flags in any other given thread (using osEventFlagsSet).
may clear its own signals or the signals of other threads (using osEventFlagsClear).

When a thread wakes up and resumes execution, its signal flags are automatically cleared (if event flags option osFlagsNoClear is not specified).

Note: The functions osEventFlagsSet, osEventFlagsClear, osEventFlagsGet, and osEventFlagsWait can be called from Interrupt Service Routines.; Refer to Event Flags Configuration for RTX5 configuration options.

Working with Events

Here is a simple example that shows how two thread can communicate with each others using event flags:

Simple event communication

The following steps are required to use event flags:

In the thread that is supposed to send a event with id sig1_id, call the wait function:
osEventFlagsSet (sig1_id, 0x0001U); // set the signal 0x0001U for thread tid_thread1
In another thread (or threads) that are supposed wait for the event:
osEventFlagsGet (sig1_id, 0x0001U, NULL, osWaitForever);

osDelay (1000); // wait for 1 second

The following complete example code can be directly used with the "CMSIS-RTOS2 main template" and is also provided as a stand-alone template for RTX5:

Code Example

void Thread_EventSender   (void *argument);                   // thread function 1
void Thread_EventReceiver (void *argument);                   // thread function 2
osThreadId_t tid_Thread_EventSender;                          // thread id 1
osThreadId_t tid_Thread_EventReceiver;                        // thread id 2
 
osEventFlagsId_t evt_id;                                      // message queue id
 
#define FLAGS_MSK1 0x00000001ul
 
void app_main (void)
{
  tid_Thread_EventSender = osThreadNew (Thread_EventSender, NULL, NULL);
  if (tid_Thread_EventSender == NULL) {
    ;                                                         // do something
  }
  tid_Thread_EventReceiver = osThreadNew (Thread_EventReceiver, NULL, NULL);
  if (tid_Thread_EventReceiver == NULL) {
    ;                                                         // do something
  }
  ;                                                           // do something
}
 
void Thread_EventSender (void *argument)
{
  evt_id = osEventFlagsNew(NULL);
  while (1) {    
    osEventFlagsSet(evt_id, FLAGS_MSK1);
    osDelay (1000);                                           // suspend thread
  }
}
 
void Thread_EventReceiver (void *argument)
{
  uint32_t flags;
  while (1) {
    flags = osEventFlagsWait (evt_id,FLAGS_MSK1,osFlagsWaitAny, osWaitForever);
    //handle event
  }
}

Data Structure Documentation

struct osEventFlagsAttr_t

Data Fields
const char *	name	name of the event flags String with a human readable name of the event object.
uint32_t	attr_bits	attribute bits No attributes available.
void *	cb_mem	memory for control block Pointer to a memory location for the event object. This can optionally be used for custom memory management systems. Specify NULL to use the kernel memory management.
uint32_t	cb_size	size of provided memory for control block The size of the memory block passed with cb_mem. Must be the size of an event object or larger.

Typedef Documentation

osEventFlagsId_t

Event Flags ID identifies the event flags.

Function Documentation

osEventFlagsId_t osEventFlagsNew ( const osEventFlagsAttr_t * attr )

Parameters

[in] attr event flags attributes; NULL: default values.

Returns: event flags ID for reference by other functions or NULL in case of error.

The function osEventFlagsNew creates a new event flags object that is used to send events across threads and returns the pointer to the event flags object identifier or NULL in case of an error.

The parameter attr sets the event flags attributes (refer to osEventFlagsAttr_t). Default attributes will be used if set to NULL.

Note: Cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
osEventFlagsId_t event_id;
  
void CreateEvent (void)  {
  event_id = osEventFlagsNew(NULL);
  if (event_id != NULL)  {
    // Event object created
  }   
}

uint32_t osEventFlagsSet	(	osEventFlagsId_t	ef_id,
		uint32_t	flags
	)

Parameters

[in]	ef_id	event flags ID obtained by osEventFlagsNew.
[in]	flags	specifies the flags that shall be set.

Returns: event flags after setting or error code if highest bit set.

The function osEventFlagsSet sets the event flags specified by the parameter flags in an event flags object specified by parameter ef_id. All threads waiting for the flag set will be notified to resume from BLOCKED state. The function returns the event flags after setting or an error code if highest bit is set (refer to Flags Functions Error Codes).

Note: This function may be called from Interrupt Service Routines.

uint32_t osEventFlagsClear	(	osEventFlagsId_t	ef_id,
		uint32_t	flags
	)

Parameters

[in]	ef_id	event flags ID obtained by osEventFlagsNew.
[in]	flags	specifies the flags that shall be cleared.

Returns: event flags before clearing or error code if highest bit set.

The function osEventFlagsClear clears the event flags specified by the parameter flags in an event flags object specified by parameter ef_id. The function returns the event flags before clearing or an error code if highest bit is set (refer to Flags Functions Error Codes).

Note: This function may be called from Interrupt Service Routines.

uint32_t osEventFlagsGet ( osEventFlagsId_t ef_id )

Parameters

[in] ef_id event flags ID obtained by osEventFlagsNew.

Returns: current event flags.

The function osEventFlagsGet returns the event flags currently set in an event flags object specified by parameter ef_id or 0 in case of an error.

Note: This function may be called from Interrupt Service Routines.

uint32_t osEventFlagsWait	(	osEventFlagsId_t	ef_id,
		uint32_t	flags,
		uint32_t	options,
		uint32_t	timeout
	)

Parameters

[in]	ef_id	event flags ID obtained by osEventFlagsNew.
[in]	flags	specifies the flags to wait for.
[in]	options	specifies flags options (osFlagsXxxx).
[in]	timeout	Timeout Value or 0 in case of no time-out.

Returns: event flags before clearing or error code if highest bit set.

The function osEventFlagsWait suspends the execution of the currently RUNNING thread until any or all event flags specified by the parameter flags in the event object specified by parameter ef_id are set. When these event flags are already set, the function returns instantly. Otherwise, the thread is put into the state BLOCKED. The function returns the event flags before clearing or an error code if highest bit is set (refer to Flags Functions Error Codes).

The options parameter specifies the wait condition:

Option
osFlagsWaitAny	Wait for any flag (default).
osFlagsWaitAll	Wait for all flags.
osFlagsNoClear	Do not clear flags which have been specified to wait for.

If osFlagsNoClear is set in the options osEventFlagsClear can be used to clear flags manually.

The parameter timeout represents a number of timer ticks and is an upper bound. The exact time delay depends on the actual time elapsed since the last timer tick.

Note: This function may be called from Interrupt Service Routines.

osStatus_t osEventFlagsDelete ( osEventFlagsId_t ef_id )

Parameters

[in] ef_id event flags ID obtained by osEventFlagsNew.

Returns: status code that indicates the execution status of the function.

The function osEventFlagsDelete deletes the event flags object specified by parameter ef_id and releases the internal memory obtained for the event flags handling. After this call, the ef_id is no longer valid and cannot be used. This can cause starvation of threads that are waiting for flags of this event object. The ef_id may be created again using the function osEventFlagsNew.

Possible osStatus_t return values:

osOK: the specified event flags object has been deleted.
osErrorISR: osEventFlagsDelete cannot be called from interrupt service routines.
osErrorParameter: the value of the parameter ef_id is incorrect.
osErrorResource: parameter ef_id is NULL or wrong.

Note: This function cannot be called from Interrupt Service Routines.

const char * osEventFlagsGetName ( osEventFlagsId_t ef_id )

Parameters

[in] ef_id event flags ID obtained by osEventFlagsNew.

Returns: name as NULL terminated string.

The function osEventFlagsGetName returns the pointer to the name string of the event flags object identified by parameter ef_id or NULL in case of an error.

Note: This function cannot be called from Interrupt Service Routines.

Code Example

void EvtFlagsGetName_example (void)  {
  char id;                                           // id of the event flags object
   
  id = osEventFlagsGetName ();
  if (id == NULL) {
    // Failed to get the event flags object name
  }
}

Data Structures

Typedefs

Functions

Description

Working with Events

Data Structure Documentation

Typedef Documentation

Function Documentation